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Professore Associato presso: Dipartimento di Ingegneria "Enzo Ferrari"

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2018 - A repertoire of failures in gudgeon pins for internal combustion engines, and a critical assessment of the design formulae [Articolo su rivista]
Strozzi, A.; Baldini, A.; Giacopini, M.; Bertocchi, E.; Mantovani, S.

The geometries commonly employed in gudgeon pins for internal combustion engines are examined. In particular, various methods for reducing the pin weight are considered. The selection of the appropriate clearance is addressed. The most typical failure modes are classified and interpreted in the light of stress analysis. The available approximate design formulae are assessed versus selected Finite Element forecasts. The fatigue cycles of stress and displacement related parameters are examined. The effect of the initial clearance on the contact pressure and on the pin ovalization is explored for selected clearance values. A typical Y-shaped fatigue crack is interpreted with the aid of Mohr circle. An error in a classical design approach based upon the containment of the pin ovalization is hypothesized.

2017 - Dynamic modal correlation of an automotive rear subframe, with particular reference to the modelling of welded joints [Articolo su rivista]
Rotondella, Vincenzo; Merulla, Andrea; Baldini, Andrea; Mantovani, Sara

This paper presents a comparison between the experimental investigation and the Finite Element (FE) modal analysis of an automotive rear subframe. A modal correlation between the experimental data and the forecasts is performed. The present numerical model constitutes a predictive methodology able to forecast the experimental dynamic behaviour of the structure. The actual structure is excited with impact hammers and the modal response of the subframe is collected and evaluated by the PolyMAX algorithm. Both the FE model and the structural performance of the subframe are defined according to the Ferrari S.p.A. internal regulations. In addition, a novel modelling technique for welded joints is proposed that represents an extension of ACM2 approach, formulated for spot weld joints in dynamic analysis. Therefore, the Modal Assurance Criterion (MAC) is considered the optimal comparison index for the numerical-experimental correlation. In conclusion, a good numerical-experimental agreement from 50 Hz up to 500 Hz has been achieved by monitoring various dynamic parameters such as the natural frequencies, the mode shapes, and frequency response functions (FRFs) of the structure that represent a validation of this FE model for structural dynamic applications.

2017 - Influence of Manufacturing Constraints on the Topology Optimization of an Automotive Dashboard [Articolo su rivista]
Mantovani, Sara; Lo Presti, Ignazio; Cavazzoni, Luca; Baldini, Andrea

Topology Optimization (TO) methods optimize material layout to design light-weight and high-performance products. However, TO methods, applied for components or assembly with high complexity shape or for structures with copious number of parts respectively, do not usually take into account the manufacturability of the optimized geometries, then a heavy further work is required to engineer the product, risking to compromise the mass reduction achieved. Within an Industry 4.0 approach, we propose to evaluate manufacturing constraints since early stages of the conceptual design to perform a TO coherent with the manufacturing technology chosen. Several approaches of TO with different manufacturing constraints such as casting and extrusion are proposed and each solution is compared. The optimum conceptual design is determined in order to minimize the component weight while satisfying both the structural targets and the manufacturing constraints; a case study on a high-performance sport car dashboard is finally presented.

2017 - On the evaluation of the peak contact stresses in a press-fitted shaft-hub coupling subject to bending [Relazione in Atti di Convegno]
Bertocchi, Enrico; Mantovani, Sara; Baldini, Andrea; Strozzi, Antonio

The peak contact stresses are addressed that are developed from the frictionless press fit of a shaft subjected to bending into an elastically similar hub with bore rounded edges. The non-linear behavior of this progressive contact is addressed by scaling a local solution available from the literature, with the aid of intermediate, auxiliary problems extracted from the fracture mechanics realm. The title problem being linear on the global domain with both the bending couple and the interference, this problem is solved by combining the FE forecasts obtained for two separate load cases, i.e. a) the interference alone and, b) the bending couple alone. Such results are expressed in terms of a) stress intensity factors for the auxiliary FM problems, and b) hoop strain component, as sampled in the proximity of the indenting edge for both the mating members. Design formulae for the contact stresses are proposed, that account for various normalized geometrical parameters, such as the outer to inner hub radii ratio, the radius of the hub bore fillet, and the contact length. Comprehensive coefficient tables are provided as well. Finally, an error analysis for the proposed method is presented.

2016 - A New Volumetric Parameter for a Comparative Finite-Element Analysis of a Six- or Four-Implant Mandibular Total-Arch Rehabilitation [Articolo su rivista]
Natali, Alfredo; Bertocchi, Enrico; Baldini, Andrea; Mulas, Giuseppe Antonio; Martinolli, Matteo; Bortolini, Sergio

In a full-arch implant rehabilitation ad modum Branemark, the distribution of stress and strain in mandibular bone is influenced by the type, number and position of implants used. In particular, the biomechanical behaviour of the bone structure after complete osseointegration depends on the load transferred to the bone by each fixture. In this study, a finite-element analysis of two models was performed. Models of an all-on-four configuration and a six-implant configuration were com- pared in a worst-case scenario. A new V parameter is presented to aid the quantitative and com- parative analysis of the all-on-four and six-implant configurations. The influence of orthotropy was also investigated, and a geometric change in the all-on-four configuration is presented.

2016 - A repertoire of failures in connecting rods for internal combustion engines, and indications on traditional and advanced design methods [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Mantovani, Sara

Several typical and uncommon failure modes in con-rods for internal combustion engines are commented from the stress level viewpoint. The interpretation of the fractures is supported with traditional calculations, with more advanced analytical models, and with Finite Element (FE) predictions. The repertoire of failures in a con-rod is presented by separately addressing the parts composing the con-rod itself, namely the shank, and the small and big ends.

2016 - Analytical evaluation of the peak contact pressure in a rectangular elastomeric seal with rounded edges [Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Mantovani, Sara; Giacopini, Matteo; Baldini, Andrea

The contact pressure is considered for an elastomeric rectangular seal with rounded edges. An asymptotic matching is performed between an available analytical expression of the contact pressure that neglects the finiteness of the seal dimensions and a fracture mechanics solution describing a periodically laterally cracked strip of finite width. This matching provides a corrected formula for the peak contact pressure that accounts for the finiteness of the seal dimensions. The analytical expression for the peak contact pressure is validated versus finite element predictions for a large family of seal geometries and, in particular, for a seal reference shape extracted from the pertinent literature. An appraisal of the finite deformation effect has been carried out numerically.

2016 - Normalization of the stress concentrations at the rounded edges of an interference fit between a solid shaft subjected to bending and a hub [Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Baldini, Andrea; Mantovani, Sara

The elastic stress concentrations are addressed that are developed from the keyless frictionless press fit of a shaft subjected to bending into a hub with rounded bore edges. Derived from a formal modeling of the title problem in terms of an integral equation, a set of normalized parameters is proposed that accounts for the combined effects on the hub stress concentration of the fillet radius, the shaft radius, the hub outer radius, the hub axial length, the interference, the Young's modulus, and the bending couple. A numerical validation of the normalized parameters is presented. With the aid of Finite Elements, various design charts are compiled that (a) forecast the bending couple initiating the detachment between the shaft and the hub, and (b) report the elastic stress concentrations within the hub versus the proposed normalized parameters in the absence of shaft–hub detachment. Such charts assist the designer in dimensioning an interference fit in the presence of a bending couple.

2016 - Parametric study of an automotive crash absorber: From analytical to FE analysis [Relazione in Atti di Convegno]
Lo Presti, I.; Vezzali, Matteo; Di Pietro, F.; Baldini, Andrea

The use of a crash absorber in a vehicle is to absorb energy. The homologation procedure of vehicles makes use of many crash tests, which are extremely expensive for car manufacturers. This discussion aims to define a methodology for crash absorber design in automotive applications. The objective is to understand the effect of geometrical parameters starting from the theory of circular and square sections. A new approach for square and rectangular sections is then created. It has therefore been possible to define a preliminary concept characterized by the main geometrical parameters such as thickness, length of the two sides and fillet radius of the section and axial length. A finite element analysis was then performed to validate this. Furthermore, a DoE analysis (Design of Experiments) was performed, explaining the influence of complex geometrical parameters such as inner plate reinforcement and indentations in order to trigger the folding mechanism.

2015 - Aluminum structures in automotive: Experimental and numerical investigation for advanced crashworthiness [Relazione in Atti di Convegno]
Miscia, Giuseppe; Rotondella, Vincenzo; Baldini, Andrea; Bertocchi, Enrico; D'Agostino, Luca

Ductility of aluminum alloys is highly used in automotive applications where crashworthiness becomes relevant. Due to its physical and mechanical properties, aluminum allows structures to be designed with good capacity to absorb energy, without increasing the overall weight of cars. In particular, high elongation allows for the conversion of a great amount of kinetic energy related to crash events in plastic deformation. If this was not the case, the energy involved during an accident could interest also the occupants, causing serious injuries. During large deformation of structures, chassis components may be subjected to failure, limiting the capacity of energy absorption. Therefore, the capability to predict the behavior of structures under crash loads becomes very important during the cars design process. Under these circumstances, finite element analysis is useful to simulate the response and to validate a project. In the last few years, prediction of materials behavior has become relevant in order to simulate in the best possible way the reaction of structures under dynamic loads. Contrary to what was expected, aluminum alloy might show anisotropic behavior after manufacturing processes. Extrusion, lamination and forging processes can modify crystallography, grains shape, precipitates and dislocations structures, affecting considerably the plastic properties. Furthermore, the failure limit strictly depends on the stress-strain state in the material during the crash event. Tensile state, shear state, compressive state and mixing states generally return different failure limits. Hence, it is indispensable to arrange a huge experimental campaign to define a thorough characterization of an aluminum alloy. Finite element (FE) codes give the possibility to include all these aspects, but several parameters need to be finely tuned. By limiting the number of tests, the present work aims at obtaining the numerical-experimental correlation of some crash absorbers during an impact. Tensile and shear specimens have been cut from the extruded parts of the chassis in 0°, 45° and 90° with respect to the extrusion direction. It is possible to define a fracture locus curve that identifies the equivalent strain limit of the aluminum alloys studied. For instance, Johnson-Cook and Bao-Wierzbicki criteria for aluminum alloys have been defined starting from a complete experimental campaign. They also give approximated analytical functions to define the entire fracture locus curve depending on the stress state. Uniaxial tensile and shear failure limits are the only ones taken into account in this work. Different hypothesis have been considered to define the rest of the fracture locus. Tuning the function parameters of the chosen criteria, a failure curve for compression, shear, tensile and mixing states have been set according to the experimental tests performed. The material card obtained has been further refined during the numerical-experimental correlation of both the samples and the crash absorbers: mesh size effects have been taken into account to assess the approximations of stress and strain into shell elements. In this work, fine mesh is only used during the initial correlation of specimens. This allows for considerably reducing the computational time of FE models studied. Acceleration signals and failures have been monitored in the crash absorbers. A high correlation between the experimental and numerical tests have validated the current methodology. Because of the few experimental tests performed on samples, it is not possible to study the exact mesh scaling effects at the beginning. Further refining is needed during the correlation of the whole component to get the right failures. In any case, the error given by the experimental dispersion could compromise the correlation and this is the reason why accuracy is not always necessary during the first phases of the correlation settings.

2015 - Analytical evaluation of the peak contact pressure in a rectangular elastomeric seal with rounded edges [Abstract in Atti di Convegno]
Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Mantovani, Sara; Strozzi, Antonio

Rectangular seals constitute an alternative design to O-rings. Rectangular seals are employed in demanding applications such as aircraft actuators, e.g. ref. [1]. The seal edges are generally rounded, ref. [2]. As a consequence of the presence of filleted edges, the contact pressure exhibits Hertzian-type local bumps in its lateral zones; it remains almost flat in the central zone of the contact. The lateral bumps and the central flattish zone confer to the contact pressure distribution a camel-backed profile, see ref. [2], and ref. [3] for a similar axisymmetric problem. It is difficult to derive a rigorous, analytical expression of the contact pressure curve for the title problem. In fact, the analytical solution available for a rectangular punch with rounded edges indenting a half plane, e.g. ref. [4] and related bibliography, is exact only in the situation of a rigid punch indenting a deformable half plane, ref. [5], whereas in the title problem the punch (i.e., the seal) is flexible and the half plane (i.e., the counterface) is rigid. It has recently been shown in refs [5-7] that the unrealities of the above analytical solution may be corrected by combining the analytical solution with Fracture Mechanics (FM) results dealing with the stress singularities at the tip of a transverse crack in a strip of finite width. In this paper, an extension of formula (20) of ref. [5] is developed, that accounts for the combined effects of a) the presence of a filleted edge, and b) a finite seal width and height.

2015 - Numerical Modeling of Aluminum Alloys Fracture for Automotive Applications [Relazione in Atti di Convegno]
Cavazzoni, Luca; Miscia, Giuseppe; Rotondella, Vincenzo; Baldini, Andrea

Nowadays, finite element analysis assumes a key-role in the automotive industry. Predictivity of FE models has been strongly improved during the last years and the research on this topic involves both industrial and academic fields. The main focus of this paper is the prediction of the failure of aluminum alloys used for extruded components. Material fracture affects the capacity of absorbing energy and the crashworthiness of the structure as well. In extracting the samples directly from the components involved in the crash event, it has been possible to take into account the whole manufacturing process. The methodology has been developed to improve the correlation of the FE models as well as to answer to the industrial requirements.

2015 - On the applicability of the Boussinesq influence function in modelling the frictionless elastic contact between a rectangular indenter with rounded edges and a half-plane [Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Baldini, Andrea; Giacopini, Matteo

The applicability of the Boussinesq influence function in modelling the frictionless elastic contact between a rectangular indenter with rounded edges and a half-plane is numerically explored. The potential of the asymptotic matching method combined with classical fracture mechanics results is investigated. Manageable design formulae for evaluating the maximum equivalent stress are analytically derived with the aid of the asymptotic matching method.

2015 - Preliminary investigation of the cavitation damage in the conrod big end bearing of a high performance engine via a mass-conserving complementarity algorithm [Abstract in Atti di Convegno]
Giacopini, Matteo; Bertocchi, Enrico; Baldini, Andrea; Strozzi, Antonio

The conrod big end bearing is one of the most critical components of internal combustion engines; it is usually subjected to high dynamic loads and high sliding velocities between contacting surfaces are often involved. Therefore, the tribological behaviour of the conrod big end bearing is often one of the key elements to engine reliability, and it has been investigated both theoretically and experimentally in several contributions in the pertinent literature [1]. With the ever-increasing quest to improve engine performance, and the consequent increase of the rotational speed and combustion/inertial loads, the cavitation of the lubricant used in conrod big end bearings may play a crucial role in the assessment of bearing durability. To overcome problems related to film cavitation, palliatives such as the reduction of the clearance between the components, the increase of the oil supply pressure and/or the use of harder coating materials have been commonly adopted. However, such simple adjustments do not always represent a valid solution; further investigations are required in order to avoid cavitation damage occurrence. The cavitation damage has been studied for more than a century both theoretically [2-5] and experimentally [6,7], and many attempts have been made to predict or measure the pressure spikes developing in the cavitated areas due to bubble collapse. Although a universally accepted theory seems not to exist, it is clear that the cavitation damage occurs due to the rapid and violent collapse of the vapour bubbles in the proximity of a solid boundary. The aim of the present work is the preliminary evaluation of the damaging effect of the cavitation in a conrod big end bearing via elasto-hydrodinamic numerical analyses.

Mulas, Giuseppe Antonio; Giacopini, Matteo; Strozzi, Antonio; Baldini, Andrea; Bertocchi, Enrico

Il comportamento tribologico e in particolare l’usura gioca un ruolo cruciale nel fallimento di una protesi d’anca. La lubrificazione dell’accoppiamento tra testa protesica e coppa acetabolare può influenzare sia la dinamica del contatto sia l’usura della protesi. Il regime di lubrificazione che governa l’accoppiamento testa-acetabolo è elastoidrodinamico. Nei diversi studi presenti nella bibliografia pertinente, raramente le analisi sono effettuate considerando la possibile cavitazione del fluido nella zona di contatto, o al più applicando una modellistica di cavitazione che si è dimostrata imperfetta in termini di conservazione della massa. Al fine di incrementare le prestazioni tribologiche di protesi d’anca, recenti studi hanno proposto l’impiego di superfici texturizzate. Attraverso l’utilizzo di un preliminare modello semplificato, viene studiata l’influenza, sul comportamento dell’accoppiamento, dei parametri geometrici che descrivono le texture. Si è utilizzato un recente algoritmo di complementarietà lineare capace di simulare il fenomeno della cavitazione conservando la massa di fluido.

2014 - Mesh morphing and fatigue analysis integration: A way to increase the industrial productivity and performance with shape optimization [Relazione in Atti di Convegno]
Cenni, Riccardo; Cova, M.; Baldini, Andrea; Cavazzuti, Marco

A methodology is developed for fatigue driven shape optimization of industrial mechanical components by means of mesh morphing. The methodology is integrated in commercial software platforms to increase its productivity and performance in industrial applications. It is well known that shape optimization is a way to improve the structural performance of components, yet it is mostly applied to linear elastic load cases. The idea of including fatigue analysis into the optimization process is of great interest for mechanical components design. Tools based on parametric geometries are becoming standard for fine-tuning optimization processes in industry. These tools can handle multiaxial fatigue analysis, but they are limited by difficulties in maintaining geometry coherence. The use of finite element models in place of parametric geometries results in a faster and more flexible methodology. In fact, mesh morphing avoids geometry coherence problems and the need of re-meshing. The aim of this work is the integration of mesh morphing and multiaxial fatigue in the context of shape optimization. A tool for achieving this was created and is presented here together with its application to part of a cast iron component subject to multi-axial high-cycle fatigue. The results obtained with the proposed methodology are closer to the industrial needs than those that can be obtained from shape optimization based on structure stiffness alone.

2014 - On the Effect of Electrodischarge Drilling on the Fatigue Life of Inconel 718 [Relazione in Atti di Convegno]
Bassoli, Elena; Baldini, Andrea; Gatto, Andrea; Strozzi, Antonio; Denti, Lucia

Difficult-to cut-materials are associated with premature tool failure, most likely in the case of complex geometries and this shapes. However, Nickel-based alloys are commonly used in high-temperature and aerospace applications, where thin deep holes are often required. Then, the only viable manufacturing solution relies on non-contact processes, like electrodischarge (ED) drilling. Morphology of ED machined surfaces is significantly different than obtained by metal-cutting operation and is known to jeopardize fatigue strength, but the extent needs to be gauged and related to the process parameters. Aim of the paper is to study the effect of holes (0.8 mm diameter, aspect ratio 10) produced by ED drilling on the fatigue life of Inconel 718. Rotating bending fatigue tests are carried out on specimens drilled under two ED setups, as well as with a traditional cutting tool. Specimens free from holes are fatigued under the same conditions for comparison. Based on previous studies, extremal ED parameters are selected, giving best surface finish versus highest productivity. S-N curves show that the ED process causes a decrease of the fatigue resistance with respect to traditional drilling, whereas the effect of different ED setups is negligible. Maximum productivity can thus be pursued with no threat to fatigue performance. The fatigue limit variation is quantified by using the superposition effect principle: ED drilling causes an increase of the stress concentration factor around 25% if compared to traditional drilling. The macroscopic fatigue behavior is integrated with a study of the effects of the different drilling processes in the micro-scale, by means of a microstructural and fractographic analysis.

2013 - A Complementarity Formulation for the EHL Analysis of a Connecting Rod Big End Bearing [Relazione in Atti di Convegno]
Giacopini, Matteo; Luca, Bertocchi; Baldini, Andrea; Daniele, Dini

In this paper, the mass-conserving formulation first proposed by Giacopini et al. in [12] and then extended in [13] to include compressibility and to study non-Newtonian fluids is further improved to consider the elastic deflection of the solid surfaces. This formulation is essentially based on a manipulation of the Reynolds equation that allows the lubrication problem in the presence of cavitation to be described as a simple Linear Complementarity Problem (LCP). In particular, this algorithm is here applied to the EHL analysis of the lubrication performance of one of the connecting rods big-end bearing of a spark ignition motorsport engine under dynamic loadings.

2013 - Achievement of a uniform contact pressure in a shaft–hub press-fit [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca

In this article, the achievement of a uniform elastic contact pressure in a frictionless, keyless, shaft-hub interference fit obtained by properly shaping the mating profiles is examined. The peculiarity of the hub mechanical response according to which, under the effect of a uniform pressure applied to the hub bore, the bore axial profile moves radially without any distortion, is exploited to simplify the determination of the mating profiles that return a uniform pressure. In particular, the hub radial deflection may be computed with a simple plane model, whereas only the shaft radial deflection requires a more complex analysis in cylindrical coordinates. Explicit approximate expressions are reported for the shapes to be conferred to the mating profiles to achieve a uniform pressure. Selected examples are presented to clarify the proposed design procedure and to preliminarily explore the effect on the pressure profile of simple shape errors.

2013 - Composite materials in automotive: Improving safety by refining FEA correlation [Relazione in Atti di Convegno]
Miscia, Giuseppe; Bertocchi, Enrico; D'Agostino, Luca; Baldini, Andrea; Dolcini, Enrico; Narducci, Angelo

In the last few years, the restrictive safety standards and the need for weight reduction have brought the crashworthiness research to focus on composite materials because of their high energy absortion-to-mass ratio. On the other hand, the possibility of obtaining predictive dynamic FEA models for these new materials is still an open issue: The present work aims at developing a methodology for the characterization of composite materials with particular interest for the head impact simulation. Composite materials behavior, defined through the mathematical models implemented in FEA codes, is very complex and requires a large amount of physical and numerical setting parameters. The majority of these parameters can be obtained by an experimental campaign that involves several kind of different tests. The presented methodology allows to obtain a good numerical-experimental correlation simply performing few tests which emulate the behavior of the component during the head impact event. A software tool based on a genetic optimization technique has been developed in order to determinate automatically the material properties values that guarantee the best numericalexperimental correlation. Copyright copy; 2013 by ASME.

2013 - Fluid film lubrication in the presence of cavitation: a mass-conserving two-dimensional formulation for compressible, piezoviscous and non-Newtonian fluids [Articolo su rivista]
Luca, Bertocchi; Daniele, Dini; Giacopini, Matteo; Mark T., Fowell; Baldini, Andrea

A mass-conserving formulation of the Reynolds equation has been recently proposed by some of the authors to deal with cavitation in lubricated contacts [1]. This formulation, based on the mathematical derivation of a linear complementarity problem (LCP), overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. In the present paper, the methodology favoured in [1], already successfully applied to solve textured bearing and squeeze problems in the presence of cavitation in a one dimensional domain for incompressible fluids, has been extended to include the effects of fluid compressibility, piezoviscosity and the non-Newtonian fluid behaviour and it has been also applied to the analysis of two dimensional problems. The evolution of the cavitated region and the contact pressure distribution are studied for a number of different configurations which can be considered as relevant benchmarks. In particular, some of the results obtained with the proposed scheme are critically analysed and compared with the predictions obtained using alternative formulations, including full CFD calculations. The stability of the proposed algorithm and its flexibility in terms of implementation of different models for compressibility, piezoviscosity and non-Newtonian behaviour are highlighted.

2013 - Full-mouth rehabilitation, a new immediate loading technique: Case report. [Abstract in Rivista]
Bortolini, Sergio; Martinolli, Matteo; Natali, Alfredo; Berzaghi, Andrea; Baldini, Andrea; Consolo, Ugo

OBJECTIVE: Today, there is evidence that, under certain conditions,  early (within 3 weeks days after surgery) and immediately (within 3 days after surgery) loaded implants have survival rates similar to delayed loaded implants. The aim of the present study is to describe an innovative clinical and technical procedure to achieve immediate loading with a complete mandibular and maxillar fixed bridge; we tested 2 different kind of abutments in the same arch to verify clinical ease of use and reliability. CASE PRESENTATION: 75 year old man, RPDs wearer. After full-mouth disinfection, in the first surgical stage the mandible was treated extracting the remaining teeth and roots. It was raised a full-thickness flap, the bone surface has been regularised, 6 implants inter-foramina were placed immediately after tooth and root extraction. 2 innovative abutments (OT Equator Profile, Rhein83, Bologna, Italy) were screwed to two implants and 4 Multi Unit Abutments (Nobel Biocare, Zürich-Flughafen, Switzerland) screwed to the others. Implant position was immediately transferred with the direct transfer technique and sterile silicone impression material (Elite Implant Medium, Zhermack S.p.a., Badia Polesine, Italy) which provides accurate implant position reproduction. A provisional prosthesis was relined directly after the suture stage, linking the provisional abutments, then refined and delivered within 6 hours. 
n a second surgical stage 8 implants were placed in the maxilla and 8 Equator Profile abutments were used. The same clinical and technical protocol used to rehabilitate the mandible was adopted. Periapical radiographs were taken immediately after implant placement, at the prosthetic phase, and at 1-year follow-up. RESULTS : In this case report the technique used to provide in few hours an immediate screw-retained fixed prosthesis allowed us to obtain satisfactory results with less effort and major ease of use than conventional procedure. After 3 years of function we had no loss of implants or prothetic problems. Patient satisfaction has improved using this protocol, probably due to the changeover from a removable to a fixed prosthesis. CONCLUSIONS: This type of implant-supported fixed prosthesis confirms its efficiency in the immediate rehabilitation of edentulous jaws. Besides less discomfort for the patient, a gain of time and a reduction in post-operative care, immediate loading has a remarkable, positive psychological impact on the patient. This technique, in the light of recent literature and evaluating ease of use and patient satisfaction, seems to be reliable in managing even complex implant cases.

2013 - Immunocytochemical and structural comparative study of committed versus multipotent stem cells cultured with different biomaterials. [Articolo su rivista]
Palumbo, Carla; Baldini, Andrea; Cavani, Francesco; Sena, Paola; Benincasa, Marta; Ferretti, Marzia; Zaffe, Davide

The aim of this work was the comparison of the behavior of committed (human osteoblast cells - hOB - from bone biopsies) versus multipotent (human dental pulp stem cells - hDPSC - from extracted teeth) cells, cultured on shot-peened titanium surfaces, since the kind of cell model considered has been shown to be relevant in techniques widely used in studies on composition/morphology of biomaterial surfaces. The titanium surface morphology, with different roughness, and the behavior of cells were analyzed by confocal microscope (CM), scanning electron microscope (SEM) and X-ray microanalysis. The best results, in terms of hOB adhesion/distribution, were highlighted by both CM and SEM in cultured plates having 20-mum-depth cavities. On the contrary, CM and SEM results highlighted the hDPSC growth regardless the different surface morphology, arranged in overlapped layers due to their high proliferation rate, showing their unfitness in biomaterial surface test. Nevertheless, hDPSC cultured inside 3D-matrices reproduced an osteocyte-like three-dimensional network, potentially useful in the repair of critical size bone defects. The behavior of the two cell models suggests a different use in biomaterial cell cultures: committed osteoblast cells could be appropriate in selecting the best surfaces to improve osseointegration, while multipotent cells could be suitable to obtain in vitro osteocyte-like network for regenerative medicine. The originality of the present work consists in studying for the first time two different cell models (committed versus multipotent) compared in parallel different biomaterial cultures, thus suggesting distinct targets for each cellular model. Copyright 2012 Elsevier Ltd. All rights reserved.

2013 - Implant-retained removable partial dentures: a 10 year retrospective study. Part I [Poster]
Bortolini, Sergio; Natali, Alfredo; Berzaghi, Andrea; Martinolli, Matteo; Baldini, Andrea; Consolo, Ugo

Objective: Aim of this study is to evaluate patient satisfaction and prosthetic complications of removable partial dentures (RPDs) retained (but not supported) by dental implants. Materials and Methods: We retrospectively evaluated 32 consecutive patients who received implant-retained RPDs. Each patient received one to four endosseus implants; the sample included a total of 64 implants. Follow-up was conducted for a minimum of 10 years, during which prosthetic complications and patient satisfaction were evaluated. Results: Our results demonstrated a systematic increase in patient satisfaction after receiving an IR-RPD. Prosthetic complications are: 4 cases of loose abutment in 3 patients; 35 tooth substitution in 25 patients; 14 adjunctive relinings (respect the conventional 1 each 2 years) in 7 patients. Conclusions: The combined use of implants and traditional RPDs increases patient satisfaction. Prosthetic complications are infrequent, easily solvable and economically less expensive for the patient.

2013 - Implant-retained removable partial dentures: a 10 year retrospective study. Part II: prosthetic complications and patient satisfaction. [Abstract in Rivista]
Bortolini, Sergio; Natali, Alfredo; Berzaghi, Andrea; Martinolli, Matteo; Baldini, Andrea; Consolo, Ugo

Objective: Aim of this study is to evaluate patient satisfaction and prosthetic complications of removable partial dentures (RPDs) retained (but not supported) by dental implants. Materials and Methods: We retrospectively evaluated 32 consecutive patients who received implant-retained RPDs. Each patient received one to four endosseus implants; the sample included a total of 64 implants. Follow-up was conducted for a minimum of 10 years, during which prosthetic complications and patient satisfaction were evaluated. Results: Our results demonstrated a systematic increase in patient satisfaction after receiving an IR-RPD. Prosthetic complications are: 4 cases of loose abutment in 3 patients; 35 tooth substitution in 25 patients; 14 adjunctive relinings (respect the conventional 1 each 2 years) in 7 patients. Conclusions: The combined use of implants and traditional RPDs increases patient satisfaction. Prosthetic complications are infrequent, easily solvable and economically less expensive for the patient.

2013 - Optimization methodology for an automotive composite hood [Relazione in Atti di Convegno]
Lazzarini, Alberto; Valgimigli, Alessandro; Baldini, Andrea; Dolcini, Enrico; Sangermano, Stefano

The current emissions regulations lead car manufacturers to look carefully for weight reduction. In the automotive industry the classic trial-and-error approach to design is becoming inadequate and techniques based on optimization are necessary to improve the design process. In this study a methodology to design a sport-car front hood is proposed. The process carried out could also be extended to car components characterised by a similar configuration. Starting from the geometry of the actual part, a design volume has been defined. The first step consists of a topology optimization performed considering the material as isotropic (aluminium properties): The output is a rough structure which accomplishes all the imposed targets. The interpretation of the topology results brings to a re-design phase aimed at realising a feasible component. The subsequent optimization step is dedicated to composite material structures and acts on the component plybook, varying thickness and orientation of each ply to find the best solution complying with targets. Finally, the component has to be reviewed from a technological point of view in order to be virtually delivered and to proceed with the prototype phase. Copyright © 2013 by ASME.

2013 - SEM Analysis of Sandblasted Double Acid Etched Titanium Implant. [Abstract in Rivista]
Bortolini, Sergio; Martinolli, Matteo; Natali, Alfredo; Berzaghi, Andrea; Strozzi, Antonio; Baldini, Andrea; Consolo, Ugo

Objective: The purpose of this work is to determine the surface morphology obtained by sandblasting and double treatment with acids of titanium implants (BioActive Treatment, B&B Dental Implant Company S.r.l., Bologna, Italy). Method: Implant surfaces are sandblasted with alumina oxide (Al₂0₃) by using a dedicated appliance. The surface is treated with a double etching by using mineral acids (phosphoric acid). Implant surfaces are cleaned with Argon plasma in a class 10.000 clean room, to guarantee the absence of environmental contamination. As an efficacy test, surfaces undergo x-ray photoelectron spectroscopy (XPS or ESCA). The surface topography of the implants was evaluated by Scanning Electron Microscope (SEM). Roughness was evaluated quantitatively using dedicated software to convert conventional SEM images into three-dimensional data (Mex 4.2, Alicona Imaging GmbH, Graz, Austria). EDX (Energy Dispersive X-ray spectroscopy) analysis was performed. Result: The SEM observation shows, in a low magnification (200x), a nice machining work, together with a homogeneous surface finish without particles or blasting residuals. Increasing the magnification, (2500-5000x) show the typical structure of micro-roughness surfaces treated with double acid attack. Values emerged from stereo SEM analysis:Ra 3.19 ± 1.06, Rq 4.78±1.15, Rt 11.41±1.06. EDX analysis confirms that the only elements detected are Ti, Al and V. Conclusion: As known and reported in the scientific literature, this micro-topography enables the surface to act as a “sponge”, interacting strongly with the clot and stimulating bone regeneration. The initial roughness level favours osteoblast cells anchor and the integration with the bone tissue, reducing the osseointegration time. With the limits of this study, this treatment seem to obtain by subtraction an implant surface with a controlled micro-roughness and absence of contaminants or foreign deposits.

2013 - Simplified modeling technique for damping materials on light structures: Experimental analysis and numerical tuning [Relazione in Atti di Convegno]
Splendi, Luca; D'Agostino, Luca; Baldini, Andrea; Castignani, Luca; Pellicano, Francesco; Pinelli, Marco

Specific polymeric and asphaltic materials are widely used for NVH automotive applications. If patches of such materials are properly collocated on vehicle's panels, they are able to improve significantly noise and vibration performance by modulating damping and stiffness. This work presents a methodology for tuning a FE composite model, using optimization techniques to improve the correlation with the experimental modal tests performed. In particular, plain and ribbed aluminum plates have been considered for several covering ratios of three damping materials. The correlation between numerical and experimental data is achieved by monitoring dynamic parameters such as natural frequencies, mode shapes, and frequency response functions (FRFs). The optimization strategy consists of two steps and makes use of evolutionary and gradient-based algorithms. LMS Virtual.Lab® is used in this part of the work as an environment for correlation and optimization. In order to verify the reliability of the correlation, modal tests are performed on a particular vehicle's panel. Copyright © 2013 by ASME.

2012 - A contribution to the Legendre series solution of the mechanical analysis of cylindrical problems [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Campioni, Eleonora; Mantovani, Sara

A series solution in terms of Legendre polynomials of the stress function suitable for modelling the mechanical response of a cylindrical component is revisited, and some contributions to the definition of the series terms are given. In particular, the correction to be imparted to a logarithmically singular series solution is considered, and a recursive approach for its determination is developed. A preliminary example dealing with an elastic, deformable cylindrical hub forced onto a rigid shaft is presented.

2012 - Stress Concentrations at the Rounded Edges of a Shaft-Hub Interference Fit Expressed in Terms of a Coefficient Normalizing the Coupling Geometry and the Young’s Modulus Effects [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca

The elastic stress concentrations developed from the keyless, frictionless, static press-fit of a solid shaft into a hub with bore rounded edges are addressed. Derived from an analytical approach, a normalising parameter Φ is employed that accounts for the combined effects on the hub stress concentration of the fillet radius of the hub bore, the shaft radius, the interference, and the Young’s modulus. Compiled with the aid of Finite Elements, several design charts are presented that report the elastic stress concentrations within the hub versus the normalising parameter Φ. Each curve is valid for prescribed ratios of a) the hub inner radius to the outer radius, and b) the fillet radius to the shaft radius. An approximating expression of ample validity is also presented for a prompt evaluation of the hub stress concentration factor.

2012 - Structural optimization of automotive chassis: theory, set up, design [Relazione in Atti di Convegno]
Cavazzuti, Marco; Splendi, Luca; D'Agostino, Luca; Torricelli, Enrico; Costi, Dario; Baldini, Andrea

Improvements in structural components design are often achieved on a trial-and-error basis guided by the designer know-how. Despite the designer experience must remain a fundamental aspect in design, such an approach is likely to allow only marginal product enhancements. A different turn of mind that could boost structural design is needed and could be given by structural optimization methods linked with finite elements analyses. These methods are here briefly introduced, and some applications are presented and discussed with the aim of showing their potential. A particular focus is given to weight reduction in automotive chassis design applications following the experience matured at MilleChili Lab.

2011 - Automotive Chassis Topology Optimization:a Comparison Between Spider and Coup´e Designs [Relazione in Atti di Convegno]
Cavazzuti, Marco; Costi, Dario; Baldini, Andrea; P., Moruzzi

Weight reduction is a major issue for carmakercompanies due the need to comply with the emission regulationswithout reducing the vehicle safety. A classic trial-and-errorapproach to design in the automotive industry is becominginadequate and new means are needed to enhance the designprocess. A major improvement on the end product can beachieved by adopting suitable optimization techniques fromthe early design stage. In the present paper the problem ofautomotive chassis design in view of weight reduction is tackledby means of topology optimization. The design methodologyproposed is applied twice: at first addressing a chassis for spidervehicles, then for coup´e vehicles. The two chassis, togetherwith some intermediate result are discussed and compared.The methodology has been proven to be successful in findinginnovative and efficient layouts for automotive chassis.

2011 - From Beam to Chassis: How to Increase NVH Performances with an Optimized Moment of Inertia Distribution [Relazione in Atti di Convegno]
Torricelli, Enrico; D'Agostino, Luca; Baldini, Andrea; P., Moruzzi

Car weight reduction is becoming more and more important for every kind of vehicle: minor mass implies, in fact, minor consumption, makes easier to fulfill homologation rules and assures a better handling behavior. Despite that, several vehicle missions have always been solved by adding more mass, e.g. NVH. In this paper, a methodology to optimize the stiffness distribution is proposed in order to obtain better vibrational performances without increasing the mass. At first, the problem has been solved for a simple beam using finite element and optimization algorithms. At a second stage, the optimal moment of inertia distribution found has been applied to a chassis thanks to a topometry optimization. Finally, the improvement in NVH performances has been verified comparing the inertances of the optimized model with those of the non-optimized one.

2011 - High performance automotive chassis design: a topology optimization based approach [Articolo su rivista]
Cavazzuti, Marco; Baldini, Andrea; Bertocchi, Enrico; Costi, Dario; Torricelli, Enrico; P., Moruzzi

Automotive chassis design in view of car weight reduction is a challenging task due to the many performance targets that must be satisfied, in particular in terms of vehicle safety. In this paper a methodology for automotive chassis design in involving optimization techniques is presented. In particular, topology, topometry and size optimizations are coupled with fem analyses and adopted in cascade for reaching an optimum chassis configuration. The methodology is applied to the design process of a rear-central engine high performance vehicle chassis. The objective of the optimization process is the chassis weight reduction, yet in fulfilment of structural performance constraints as required by Ferrari standards. The results demonstrate the general applicability of the methodology presented for obtaining the general trusses layout and thicknesses distribution of the structure. The numerical model at this stage shows a significant weight reduction when compared to the chassis of the Ferrari F458 Italia.

2011 - Maximum equivalent stress in a pin-loaded lug in the presence of initial clearance [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca

Various design charts of ample validity and prompt access are presented, which permit the contact stresses within the lug of a pinned connection to be forecast in the presence of an initial clearance between the pin periphery and the lug bore. To cover the range of the practically encountered geometries and loadings, round-ended lugs of various widths and with a variously tapered shank are considered, and several inclinations of the applied load are addressed. The charts are compiled with the aid of finite elements. The employment of the recently proposed load factor Φ allows the combined effects on the peak contact stresses of the load intensity and of the initial clearance to be predicted.

2011 - Normalization of the stress concentrations at the rounded edges of a shaft–hub interference fit [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca

The elastic stress concentrations developed from the keyless frictionless static press-fit of a shaft into a hub are addressed. Two configurations are examined, namely (a) an infinitely long solid shaft press-fitted into a hollow hub with bore rounded edges, and (b) a shaft with filleted extremity, partially inserted into a hub. Derived from an analytical approach, a normalizing parameter is proposed that accounts for the combined effects on the stress concentrations of the fillet radius, the shaft radius, the interference, and Young’s modulus. With the aid of finite elements, various design charts are compiled that report the elastic stress concentrations within the hub versus the proposed normalizing parameter. Each curve is valid for a fixed ratio of inner to outer hub radii.

2011 - RGB method in immunofluorescence investigations on stem cells [Articolo su rivista]
Riccio, Massimo; E., Resca; Bertoni, Laura; Cavani, Francesco; Sena, Paola; Ferretti, Marzia; Baldini, Andrea; Palumbo, Carla; DE POL, Anto

Colour is not related to a particular discipline, but it is transversely present in many circles and inalmost all the aspects of life. It has a special value in art, but also as far as other disciplines areconcerned, like the sciences, the colour is at the basis of some of their intrinsic significances and it oftenneeded to allow the interpretation of some of their phenomena as well. As regards the development ofcell biology knowledge, colour acquired more and more importance in revealing the observations of theresearchers. A field in which the methods based on the colours are particularly employed is theimmunofluorescence, used to identify specific proteins in cells and tissues. These techniques combinethe fluorochrome properties with specific molecules, i.e. antibodies, directed against particularsubstances to investigate, for example a specific protein. In single immunofluorescence analysis, thesignal from an excited fluorochrome corresponds to a particular protein. In multiple immunofluorescenceanalysis, two or more signals are simultaneously detected to show the localization of differentproteins on the same sample. The three primary colours red, green and blue were currently assigned tothe signals from immunofluorescence-processed samples and visualized by the RGB method. In thepresent work, different examples of RGB applications in immunocytochemical investigations areshowed: the first concerns the multiple analysis of three markers, localized in different loci of the cellplasma membrane; the second is related to the co-localization of two signals in the same site of specificsubcellular structures. In this case the secondary colours, obtained by overlapping the primary ones,demonstrate the specific co-presence of two proteins in the same site. With the present paper, theauthors wish to underline the relevant role of colours also in those areas in which colours are the meansnot the end.

2011 - Torque Transmission by Friction in a Keyed Shaft-Hub Press-Fits [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca; Campioni, Eleonora; Mantovani, Sara; O., Quareshi

Interference fits are widely employed to semi-permanently connect gears, pulleys, flanges, wheels, disks, rotors, and similar mechanical components, to a shaft. The stress state along the hub central portion may be thoroughly predicted by modelling the press-fit problem as plane and by employing the Lamé equations for thick-walled cylinders, and the transmissible torque may be confidently estimated by relying on the Lamé predictions, since they are valid along most of the contact axial length. Often a key is added to the press-fit, to secure the torque transmission and to prevent any relative rotation between the shaft and the hub. Both parallel and tapered keys are employed in practical applications. With respect to their tapered counterparts, parallel keys possess the advantage that they do not cause any eccentricity. This study considers parallel keys only. The presence of the keyseat increases the compliance of the hub and the shaft, thus producing a diminution of the contact pressure between the hub and the shaft, which results in a similar diminution of the transmissible torque. In this paper, a preliminary Finite Element analysis is carried out to quantify the above diminution of the contact pressure in the assumption of frictionless contact. The analysis is carried out for a solid shaft and for a practically relevant selection of ratios between the hub inner and outer radii. A preliminary development is presented of an analytical approach based upon the classical Michell polar solution, which is particularly suitable to mimic rings. The diminution of the transmissible torque with respect to a keyless shaft-hub press-fit is quantified, and the results are presented in a design diagram.

Natali, Alfredo; C., Pirondi; Bortolini, Sergio; E., Campioni; Bertocchi, Enrico; Baldini, Andrea; Consolo, Ugo


2010 - Automazione e Verifica del Processo di Incollaggio in Linee Produttive di Telai per Vetture d’Alta Gamma [Abstract in Atti di Convegno]
Andrisano, Angelo Oreste; Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Leali, Francesco; Mantovani, Sara; Pellicciari, Marcello; Pini, Fabio; Strozzi, Antonio; Vergnano, Alberto

Sommario. La produzione industriale dei telai auto ha registrato, nel tempo, una grande evoluzione progettuale e tecnologica, spinta dalla necessità di garantire alte prestazioni e comfort elevato, nel rispetto della sicurezza dei passeggeri e della sostenibilità ambientale. Le linee produttive di assemblaggio sono, soprattutto in segmenti di fascia alta, progettate per l‟esecuzione, su telai diversi, di articolati processi ibridi di giunzione, basati, cioè, sull‟adozione di tecnologie di saldatura, rivettatura ed incollaggio. I sistemi che ne derivano sono, dunque, caratterizzati da elevata complessità e richiedono lo sviluppo di dispositivi automatici dedicati e l‟impiego simultaneo di robot industriali e risorse umane. La soluzione di tali problematiche richiede l‟intervento sinergico di vari settori dell‟Ingegneria Meccanica poiché coinvolge competenze metallurgiche, progettuali e tecnologiche. A queste si aggiungono le competenze necessarie alla progettazione di sistemi produttivi ad alta flessibilità che, secondo la visione proposta dagli autori, siano caratterizzati da elevata modularità strutturale ed operativa, parametricità e standardizzazione delle soluzioni progettuali e dei componenti, autonomia esecutiva, e che assicurino una rapida ed efficace riconfigurazione, garantendo, parallelamente, l‟alto livello qualitativo dei prodotti ed il completo controllo dei processi realizzati. Il presente articolo tratta lo sviluppo e la progettazione integrata del modulo robotizzato di incollaggio per linee di assemblaggio ibride di telai in alluminio, svolta in collaborazione con il gruppo ALCOA e con SIR SpA. Successivamente vengono presentati i risultati sperimentali ottenuti dalla verifica strutturale a lap shear e peeling di alcuni provini ricavati da assemblati del tunnel, effettuata secondo normative interne Ferrari SpA. Abstract. In the last years, industrial production of automotive chassis has gained a great evolution in design and technology, spurred by the need to achieve high performance and comfort, while ensuring both the safety of passengers and the environmental sustainability. State-of-the-art assembly lines, especially in top class segments, are designed to employ hybrid junctions on different chassis. Such complex process is based on the simultaneous adoption of welding, riveting and adhesive bonding technologies. The production systems design engages the development of specific automated devices and the cooperation of industrial robots and human resources. The solution of these issues involves the synergic action of various sectors of mechanical engineering, as metallurgy, design, and mechanical technology. Design of high flexibility production systems is another important issue: according to the viewpoint proposed by the authors, such systems are characterized by high structural and operational modularity, by parametric and standard design of solutions and components, by executive autonomy and rapid reconfiguration capability, thus simultaneously ensuring high quality of products and the complete control of processes. The present paper deals with the development and integrated design of the robotic adhesive bonding module in hybrid assembly lines for aluminum chassis, carried out in collaboration with the ALCOA group and SIR SpA. Experimental results are also presented, that refer to lap shear and peeling tests, carried out on specimens extracted from the chassis tunnel, according to Ferrari SpA internal standards.

Natali, Alfredo; C., Pirondi; Bortolini, Sergio; E., Campioni; Baldini, Andrea; Bertocchi, Enrico; Consolo, Ugo

Purpose: A recent procedure called “All-on-four " provides the rehabilitation of atrophic edentulous jaws by means of a fixed prosthesis supported by 4 implants. Purpose of this work is the comparative evaluation between the biomechanical features of the All on Four versus traditional therapyMethods: it was created a 3D model (SolidWorks - Dessault Systems SolidWorks Corp - Concord, MA, USA) of a clinical case with 6 mandibular implants and a screwed framework. The FEM analysis was performed by varying the number and position of the implants and the superstructure material. 9 different models were analyzed. The load was 300 N on the distal part of the framework.Results: Implants closest to the application of the force are the more loaded. In the superstructure there was a stress peak that exceeds the plasticization value of one material (titanium), although the area is very limited. In the bone, maximum stress occurs in the cortical component, while the medullary component is less interested. The distal implant (closer to the force) has a compressive load, while the mesial one has a tractive stress.Conclusion: The strategic distribution of implants appears to be the key factor that governs the distribution of loads. A limited number of implants, strategically placed, can be an effective alternative rehabilitation in selected cases. This suggests a possible effectiveness of the fixed implant prosthesis on 4 implants, accompanying the reduction of, costs, post-operative morbidity and the difficulty of the prosthesis than other procedures.

2010 - Preliminary plane mechanical modeling of hexagonal contact [Relazione in Atti di Convegno]
Strozzi, Antonio; Radi, Enrico; Baldini, Andrea; Giacopini, Matteo; Campioni, Eleonora

A hexagonal joint is mechanically analysed. A cross section of the contact between male and female components is modelled as a plane strain problem, and the contact and detachment zones are investigated with two approaches, a) an analytical study formulated in terms of an integral equation; b) a FE analysis. Preliminary results refer to the situation of null initial clearance and coefficient of friction. For each side of the hexagonal contact, the contact zone constitutes a small portion of the length of the hexagonal side, since separation occurs along a sizeable side length.

2010 - Sport car space-frame chassis design in view of weight reduction [Relazione in Atti di Convegno]
Torricelli, Enrico; Costi, Dario; Baldini, Andrea; Bertocchi, Enrico; P., Moruzzi

Road vehicle homologation has become more and more challenging due to the introduction of stringent regulations regarding pollutant emissions. In order to fulfil these requirements, the focus in automotive industry mainly settled on the improvement of the engine performance in terms of fuel consumption. Another design approach aims at the vehicle lightening, yet in the respect of the safety standards. In the present work a methodology for preliminary space-frame chassis design for rear-central engine sport cars is proposed. The purpose is to design a chassis able to attain given performance goals in view of weight reduction. The design problem is faced using finite element analysis. The chassis numerical model is made of shell elements and is split into three sub-models: front, central, and rear. This allows the parallelization of the work among different teams. The sub-models undergo topometry and size optimizations in order to asses the optimal shell thickness distribution.

2009 - Contact stresses within a split ring inserted into acircular housing [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto; Bertocchi, Enrico

The contact problem between a split ring and a circular housing is mechanicallyexamined. This contact is revisited in terms of receding contact, the zones along which the ringbeds over the housing are investigated, and normalizing design parameters are evidenced. Thesplit ring is modelled in terms of a straight, purely flexural beam as well as of a curved, shearelasticbeam; for both models, analytical solutions are obtained. Various easy accessible designdiagrams, useful for estimating the maximum elastic stresses within the split ring and the axialinsertion force, have been prepared with the aid of these two beam models and using finiteelements. The mechanical response of the split ring when its angular width is appreciably lowerthan p is clarified.

2009 - Influence of the initial clearance on the peak stress in connecting-rod small ends [Articolo su rivista]
A., Pioli; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto

The stress increase that is caused by the presence of an initial clearance within thesmall end of connecting rods for motorbike and car engines is investigated. Plane analyticaland numerical modellings of the dry contact between the small-end and piston pin areadopted. Based upon a recent analytical result, a normalizing parameter is introduced, whichallows the stress concentration factor at the small-end bore sides to be expressed as a functionof a proper combination of the initial clearance between the small end and gudgeon pin, theapplied load, and Young’s modulus, for prescribed aspect ratios of the small end and hollowpin. Design diagrams summarizing the consequences of an initial clearance between the smallendbore and gudgeon pin on the eye peak stress are reported, which cover a wide range ofgeometries, clearances, and loadings. Selected comparisons between two-dimensional andthree-dimensional models are carried out.

2009 - Materials selection criteria for the weight reduction of high performance sports car [Articolo su rivista]
Veronesi, Paolo; Pivetti, A; Baldini, Andrea; Loiacono, M; Poli, Giorgio

For high-performance luxury cars, the first element of competitiveness isgiven by the dynamic performances. Thus, weight reduction is becoming increasinglyimportant, also in the framework of the introduction of more andmore restrictive regulations on emissions. Designers are currently focusingon maximizing the power/weight ratio, and the proper material selectionbecomes mandatory. This paper describes the weight reduction achievable onthe suspension system of a Lamborghini Murcielago, showing that the useof high strength low alloy steels as well as titanium and aluminum alloysallows to reduce weight of selected components of more than 30%.Three different components of the suspension system have been analyzed:the front lower arm (fig. 1), the front suspension spring (Table II) and theanti-roll bar (fig. 5). According to the method proposed by M.F. Ashby [2],the design requirements have been translated into a series of constraints,objectives and free variables, leading to the definition of material indexes(equations 1-8) to be used to rank the materials in order to identify the mostsuitable ones. Ranking was accomplished using the CES (Cambridge EngineeringSelector, Granta-design) software, which allows to create selectioncharts like the ones shown in Fig. 2, 3, 4, 6. Those diagrams help the designerto select graphically the candidate materials for the application, which, forthe studied cases, resulted to be:- Low alloy steels or aluminum alloys (Table II) for the front lower arm- Titanium or spring steel(fig. 1), for the front suspension spring- Aluminum alloy for the anti-roll barDimensioning of the components on the basis of the selected materials ispresented as well, demonstrating that a proper materials selection procedureallows to significantly decrease the weight of the studied components withrespect to the current solutions.

2009 - Three examples of inadequacy of the Williams asymptotic method in predicting the singularity strength in elastic problems [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto

Three examples are presented for which the Williams asymptotic method appears to be inadequate in forecasting the strengh of the singularity encountered in elastic problems. The first case addresses a Kirchhoff plate resting on an irregular linear support; the second example revisits a classical plane elasticity contact problem; the third case considers an infinite sheet with a square hole. The reasons of the inadequacy of the Williams asymptotic method in treating the above situations are discussed.

2008 - Astra Research [Spin Off]
Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto; A., Salsi

2008 - Biomechanical aspects in dental replacements [Capitolo/Saggio]
Baldini, Andrea; Bruzzesi, G.; Zaffe, Davide; Giacopini, Matteo; Strozzi, Antonio; De Pol, Anto

This chapter deals with biomechanical aspects in dental replacements. The state of the art is critically reviewed taking into account the body of the literature results. The initial section is devoted to the mechanical properties of bone and to a description of the jaw geometry and of its loading and constraining. The following section presents a classifi cation of the various tooth replacement confi gurations and of the various materials adopted, where single and multiple replacements are considered. A specifi c section is devoted to the solid modelling of the jaw as input to numerical analyses, where the aid offered by reverse engineering and tomography is underlined. The fi nite element method as well as alternative numerical and experimental approaches are reviewed in a dedicated section. The stress analysis forecasts and measurements are biomechanically interpreted in the light of the current literature results. The chapter ends with a section devoted to biological aspects.

2008 - Human dental pulp stem cells (HDPSC) versus osteoblast-like cells: comparison for capability of adhesion, growth and bone matrix formation on differently-shaped surfaces of biomaterials. [Abstract in Rivista]
Palumbo, Carla; Riccio, M.; Resca, E.; Bretoni, L.; Ferretti, Marzia; Cavani, Francesco; Bruzzesi, G.; Baldini, Andrea; DE POL, Anto

Comparisons between HDPSC and osteoblast-like cells are made in regards to bone matrix production as well as distribution, density and adhesion to the biomaterial surfaces.

Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Margini, Stefano; Rivasi, Stefano; Rosi, Roberto; Strozzi, Antonio

In the paper, the authors discuss possible causes of conrod torsional vibrations. Several simplified models are laid out for prediction, evaluation and future research. Some critical remarks about these prospective models are presented. Comparisons with a limited number of experimental cases is finally provided.

2007 - Adult human dental pulp stem cells (DPSC): preliminary observations for selecting and conditioning DPSC according osteogenic aims. [Abstract in Rivista]
Palumbo, Carla; Riccio, Massimo; Resca, Elisa; Bertoni, Laura; Baldini, Andrea; Strozzi, Antonio; G., Bruzzesi; DE POL, Anto

The previlinary observations have shown the possibility to obtain in vitro bone formation to apply in regenerative medicine.

2007 - Maximum Stresses in a Taper-shanked Round-ended Lug Loaded by an Oblique Concentrated Force [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rivasi, Stefano; Rosi, Roberto

In this study, the stress state in a round-ended, taper-shanked lug loaded by an oblique point force is investigated. Numerical, analytical and, partially, photoelastic studies were carried out. In the analytical model, the lug is modelled as a plane problem, and it is partially likened to a ring examined with a Michell-type series solution; the differences in shape between lug and ring are overcome by endowing the series solution with degrees of freedom suitable for adapting the ring solution to the lug actual geometry. Three prompt access design charts are presented, which report the normalised stress concentration for three lug shank taper angles, for selection of five aspect ratios between bore radius and radius of the rounded extremity, and for load inclinations ranging from longitudinal to transverse directions

M., Ciavarella; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo

A normalizing loading parameter useful in summarising the mechanical response ofplane pin-in-plate-like contacts is extended to axisymmetric ball-in-socket-like contacts. Anexample addressing a compliant layered artificial hip joint is presented, and the usefulness ofthe normalizing loading parameter is evidenced.

2006 - Maximum equivalent stress in a pin-loaded lug subject to inclined loading [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; M., Nascimbeni

The elastic maximum equivalent stress in a pin-loaded, straight- or taper-shanked, round-ended lug subject to inclined loading is investigated using the finite element and the boundary element methods, and, partly, photoelasticity. The influence of the load direction, of the ratio between the bore diameter and lug width, and of the shank taper angle are particularly addressed. In addition, the effects of the axial length of the lug trunk and, partially, of the initial clearance between the lug bore and pin are numerically examined in the presence of a loading variously inclined to the lug axis. An interpolating expression for the maximum equivalent stress as a function of the ratio between the bore diameter and lug width, taper angle, and load inclination angle is proposed.

2006 - On the Applicability of the Loading Parameter PHI in Pinned Connections with Relevant Initial Clearance [Relazione in Atti di Convegno]
Ciavarella, M; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rivasi, Stefano; Rosi, Roberto

In pinned connections, the presence of an initial clearance increases the lug stress concentration with respect to a neat fit configuration. By employing a recently proposed loading parameter Φ valid for plane models, the applied load and initial clearance effects on the stress concentration are normalised for a straight-shanked, round-ended, longitudinally loaded pin-lug connection of fixed outer to inner radius ratio. Results are obtained with a Mitchell-type, Fourier series solution and with commercial Finite Elements. The applicability of the loading parameter Φ to pinned connections with small to relevant initial clearances is explored. Two preliminary design charts are presented, which quantify the lug stress concentration factor versus the loading parameter Φ for two lug geometries defined by inner to outer radii ratios of 0.376 and 0.77.

2006 - Reduced dependence on loading parameters in almost conforming contacts [Articolo su rivista]
M., Ciavarella; Baldini, Andrea; J. R., Barber; Strozzi, Antonio

In cases of completely conforming frictionless contact, the contact area generally either decreases or stays the same under load, in which case the extent of the contact area is subsequently independent of load and the stress and displacement fields vary linearly with the loading parameter. Dundurs and Stippes describe such cases as receding contact problems. Here, we demonstrate that similar results apply in the presence of Coulomb friction, in which case the extent of the stick and slip zones and the local direction of sliding are independent of load. We also show that if there is a small initial gap or interference throughout the potential contact area, the extent of the contact area and the stress and displacement fields will approach those of the corresponding receding contact problem as the applied load is increased. If the interface conditions permit adhesion between the contacting surfaces, the extent of the adhesion zone shrinks to zero as the load increases without limit. Progress of the contact configuration towards the limit is governed solely by a dimensionless load factor involving the ratio between the applied load and the initial clearance or interference. This permits results for a variety of initial geometries (due to tolerance variations) to be obtained from a set of finite element results for a single case. Some of these characteristics are demonstrated using a finite element solution of a connecting rod/bushing/gudgeon pin contact. Other interesting applications are those with complex geometries, ranging from biomechanics, as in prostheses, to the design of multiple fasteners. (C) 2006 Elsevier Ltd. All rights reserved.

2005 - Optimization of a Cooling Circuit in an Internal Combustion Engine for Marine Applications [Relazione in Atti di Convegno]
Cantore, G.; Fontanesi, S.; Gagliardi, V.; Malaguti, S.; Baldini, A.; Giacopini, M.; Strozzi, A.; Rosi, R.

An optimization study involving both fluid-dynamic and thermostructural aspects has been carried out for a 2200 cc turbocharged engine head for marine applications. In this cross-disciplinary problem, the structural and thermodynamic aspects have been decoupled. A preliminary set of CFD numerical analyses of the cooling jacket layout has been performed, in order to investigate critical aspects of the present configuration and improve the cooling performance, by means of local flow patterns and flow distribution analysis. At a second stage, temperature distributions within the metal cast parts have been derived from CFD in order to assess the fatigue strength of the component with structural finite elements. A proper choice of both CFD methodology and boundary conditions is carried out in order to determine a trade-off between computational effort and actual engine behavior representation. The proposed modelling procedure allows a sensitivity study to be carried out of the engine head to variations of the leading geometric parameters, thus devising an optimized component. The methodology favored in this study is finally applied to carry out a comparison between the basic configuration and a fluid-dynamic improved solution, in order to estimate the effectiveness of the design optimization on the fatigue strength of the component.